Low power sensors as level measurement and detection/switching sensors for liquids and solids incorporating a two wire control loop as a Namur interface operate at very low power requirements in a range below 1.2 mA at 5 V. The energy provided in the sensor is sufficient for level detection. However, if a further component as e.g. an adjustment unit would have to be connected to the sensor, as it would be the case for e.g. an adjustment or setting of the sensor, then, the energy provided in the sensor would not be sufficient to also energize this additional external component, e.g. the adjustment unit, connected thereto.
In a modular system, as it is concerned in the present invention, a modular display and adjustment unit connectable to the modular low power sensor unit would require an additional power source to cooperate, i.e. to input, output or process data. Measurement devices comprising sensors, additional external components and a single power supply are described e.g. in WO 00/50847 A1, DE 195 47 281 A1 and DE 101 13 646 A1, without providing a single power supply device that energizes simultaneously low power sensors and the external components. Common power supplies for low power circuits, described e.g. in WO 1993/004422, are just capable to regulate the input power for energizing low power sensors without providing interfaces for adapting and energizing external components. However, since the system is modular, the display and adjustment unit can also be used together with other sensor units, like e.g. continuously operating sensors in the range of 4-20 mA. These supply sufficient energy to also energize the display and adjustment unit without any further external or additional internal power source. Therefore, it would be meaningful to provide a power supply device which can be used in the modular system to provide both the power for the display and adjustment unit as well as for the additional power needed for the low power sensor unit to cooperate with the display and adjustment unit when it is connected to the sensor.
Moreover, there would be an additional power requirement within the low power sensor unit itself, e.g. for the processing of data received from the component connected thereto and for data communication between the low power sensor unit and the component connected thereto, like a display and adjustment unit as mentioned above.